Study of the amoxicillin and amoxicillin-clavulanate resistance involved in 231 Escherichia coli clinical strains isolated in 1992 at Cochin hospital.

Among 231 clinical strains of Escherichia coli tested during may 1992, 89 isolates (38,5 %) were resistant to beta-lactams. The resistant strains were principally recovered from urinary and genital specimen from medicine and surgical departments. MICs of beta-lactams were determined alone or combined with clavulanic acid, and beta-lactamases were identified by isoelectric point characterization and by enzymatic inhibition tests. Among the resistant strains, 92,1 % were secreting a penicillinase and 6,7 % a cephalosporinase. No extended-spectrum beta-lactamase was observed. 85,5 % of penicillinases were TEM-1 enzymes, 4,9 % SHV-1 beta-lactamase, 1,1 % oxA-1 p-lactamase and 8,5 %, 7 strains, were IRT beta-lactamases (formerly called TRI). For 24 clinical E. coli strains, the MICs values were greater than or equal to 32 mg/l for amoxicillin plus clavulanic acid. The 7 IRT beta-lactamases showed the highest MICs, 256 to 4096 mg/l. Four of them exhibited a beta-lactamase of pI 5,4 and 3 a beta-lactamase of pi 5,2. The IRT beta-lactamases represent 3 % of all the Escherichia coli strains. This frequency is comparable or lower than the values reported by other studies conducted between 1992 and 1994.